#include<iostream>
//#include<string>
//#include<cstdio>
//#include<cstring>
//#include<cmath>
//#include<algorithm>
using namespace std;

long long a[50];

int main()
{
    int k;
    cin>>k;
    a[1]=1;
    a[2]=2;
    for (int i=3;i<=k;i++)
    	a[i]=a[i-1]+a[i-2];
    cout<<a[k]<<endl;
    
    return 0;
}